glSelectBuffer has two arguments: buffer is a pointer to
an array of unsigned integers, and size indicates the size of the array.
buffer returns values from the name stack (see glInitNames, glLoadName,
glPushName) when the rendering mode is GL_SELECT (see glRenderMode). glSelectBuffer
must be issued before selection mode is enabled, and it must not be issued
while the rendering mode is GL_SELECT.

A programmer can use selection to
determine which primitives are drawn into some region of a window. The region
is defined by the current modelview and perspective matrices.

In selection
mode, no pixel fragments are produced from rasterization. Instead, if a
primitive or a raster position intersects the clipping volume defined
by the viewing frustum and the user-defined clipping planes, this primitive
causes a selection hit. (With polygons, no hit occurs if the polygon is
culled.) When a change is made to the name stack, or when glRenderMode is
called, a hit record is copied to buffer if any hits have occurred since
the last such event (name stack change or glRenderMode call). The hit record
consists of the number of names in the name stack at the time of the event,
followed by the minimum and maximum depth values of all vertices that hit
since the previous event, followed by the name stack contents, bottom name
first.

Depth values (which are in the range [0,1]) are multiplied by 2^32
- 1, before being placed in the hit record.

An internal index into buffer
is reset to 0 whenever selection mode is entered. Each time a hit record
is copied into buffer, the index is incremented to point to the cell just
past the end of the block of names - that is, to the next available cell.
If the hit record is larger than the number of remaining locations in buffer,
as much data as can fit is copied, and the overflow flag is set. If the
name stack is empty when a hit record is copied, that record consists of
0 followed by the minimum and maximum depth values.

To exit selection mode,
call glRenderMode with an argument other than GL_SELECT. Whenever glRenderMode
is called while the render mode is GL_SELECT, it returns the number of
hit records copied to buffer, resets the overflow flag and the selection
buffer pointer, and initializes the name stack to be empty. If the overflow
bit was set when glRenderMode was called, a negative hit record count is
returned.